Age Replacement Models with Random Works

Abstract

This chapter gives four age replacement models for an operating unit when it works successively for jobs with random working cycles: (1) The unit is replaced at a total operating time T; (2) the unit is replaced at a total operating time T or at a random working cycle Y, whichever occurs first; (3) the unit is replaced at a total operating time T or at a random working cycle Y, whichever occurs last; and (4) the unit is replaced at the first completion of some working cycles over a planned time T. As a particular case of (2)–(4), random replacement, where the unit is replaced only at a random working cycle Y, is considered. Optimal policies for each model are discussed analytically, and Polices (2)–(4) are compared with (1) from the viewpoint of cost rate to find that Policy (1) is the best when preventive replacement costs are the same. However, random replacement and Policy (4) should be better than standard policy when a lower random replacement cost is supposed.